As a substrate for a high-density recording medium such as a hard disk, a glass blank, which is a thin-plate like glass molding product, is used. In general, the glass blank is produced by shaping a block (gob) of heated and melted glass, while pinching the gob between an upper mold and an lower mold and cooling the gob, using a device described in Japanese Patent Publication No. 3709033 (hereafter, referred to as patent document 1). Specifically, the gob is dropped on the lower mold, and then the upper mold is driven toward the lower mold, thereby pressing the gob between the upper mold and the lower mold. In addition, in order to improve mold separability of the glass blank, temperatures of the upper mold and the lower mold are set near a glass transition temperature of the gob.
Further, in the device described in patent document 1, in order to produce the glass blank efficiently, a plurality of lower molds are prepared for one upper plate. After the shaping of the glass blank between the upper mold and one of the plurality of lower mold has been finished, the upper mold is separated from the lower mold and performs shaping of another glass blank with another lower mold. The glass blank is taken out from the lower mold which has been separated from the upper mold, and the lower mold is cooled. Then, at a next step, the glass blank is polished and cut, thereby forming a disk-shaped substrate for recording information, which is shaped in a true circle, and whose surface is finished like a mirror surface. An information recording medium (a platter of a hard disk) is formed through forming an information recording layer, such as a layer of a magnetic material, on the substrate for recording information.